05 March, 2021

Plant cognition






  • Do plants sense their environment?
    • changes in essential resources
    • herbivory/disturbance
    • external stimulus


  • If so, what do they do about it?
    • do plants process information?

Sensory cell systems


  • Cell to cell signal networks


  • Ca2+ based signals are common

Wounding triggers transmission of Ca2+ to start defense


Plants grow towards light: Phototropism via Auxin

Plants competing for light can grow really tall




  • Primary and secondary growth allow trees to be giants


  • Are their limitations to plant height?
    • Redwoods = 116 m


  • What resource most limits growth?

Plant Water Transport: Soil - Root - Stem - Leaf - Air

Are there limits to moving water?



  • Large trees move hundreds of gallons of water a day
    • only small amounts needed for growth/photosynthesis


  • Gravity
    • harder and harder to move water
    • xylem less efficient @ top
    • theoretically, limits growth to 122-130 m


  • Drying soil adds opposite tension

How long a straw could Superman use?

How can redwood trees grow so tall?


  • Cohesion tension theory
    • plants use water properties to cheat gravity


  • Cohesion: H20 stick to other H20 molecules
    • via H bonds


  • Adhesion: water sticks to non water molecules
    • stick to sides of xylem tissues
    • H20 not pulled straight up!


  • Transpiration pulls water under tension

How can redwood trees grow so tall?



  • H2O also pulled in zig zag motion
    • pits and perforations
    • tracheids are twisted


  • Vascular tissue is tough
    • high resistance of lignified walls
    • built not to collapse


  • Redwoods near theoretical limit!

Cavitation: When water breaks

How plants avoid water problems: Close stomata

Risky stomatal behavior

How plants avoid water problems: Refill Soil

How plants avoid water problems: Alter xylem cells